Welded header and tube assembly for steam generators



June 2, 1970 w. v. HAMBLETON EI'AL 3,515,101

WELDED HEADER AND TUBE ASSEMBLY FOR STEAM GENERATORS Filed Aug. 2, 1968 1 3 Sheets-Sheet 1 INVENTOR WARNER V. HAMBLET N DEAN P. UNTHANK BY Z/ /ZQ ATTORNEY June 2, 1970 w. v. HAMBLETON ETA!- 3,515,101

WELDED HEADER AND TUBE ASSEMBLY FOR STEAM GENERATORS Filed Aug. 2, 1968 3 Sheets-Sheet 2 42 F 6' 7 W INVENTORS WARNER V. HAMBLETON DEAN R UNTHANK A TTORNE Y June 2, 1970 w, v, HAMBLETQN ETAL 3,515,101

WELDED HEADER AND TUBE ASSEMBLY FOR STEAM GENERATORS Filed Aug. 2, 1968 3 Sheets-Sheet 5 INVENTO WARNER V. HAMBL E ON BYDEAN P. UN THANK M fl A T TORNE Y United States Patent O l 3,515,101 WELDED HEADER AND TUBE ASSEMBLY FOR STEAM GENERATORS Warner V. Hambletou, Dallas, Tex., and Dean P. Unthank, Louisville, Ky., assiguors to Henry Vogt Machine Company, Inc., Louisville, Ky., a corporation of Kentucky Filed Aug. 2, 1968, Ser. No. 749,720 Int. Cl. F22b 37/22 US. Cl. 122365 Claims ABSTRACT OF THE DISCLOSURE Discloses a welded header and tube assembly designed for use in water tube, natural circulation steam generators, utilizing modular banks of heat exchange tubes. Discloses upper and lower horizontally disposed cylindrical tubular headers in communication with one or more rows of vertically oriented heat exchange tubes, forming modular tube banks, in which the upper and lower ends of the heat exchange tubes project through the walls of the upper and lower cylindrical headers, respectively, and in which the major axes of said tubes are parallel to the vertical center line of said headers to communicate with the bores or interior cavities of said headers. In a preferred embodiment, the rows of tubes are laterally spaced from and parallel to the vertical centerline of the headers.

FIELD OF THE INVENTION This invention relates to steam generators, and more particularly, to steam generators of the natural circulation, water tube type. More specifically, this invention relates to welded header and tube assemblies, forming modular banks of shop assembled heat exchange tubes for use in steam generators. Still more specifically, this invention relates to an improved welded tube and header connection, used in forming modular tube banks.

DESCRIPTION OF THE PRIOR ART An early method of tube and header connection, which is still used today, involves the technique of rolling heat exchange tubes into headers or drums. With drums, which have a large enough internal diameter to allow a man access, the tube ends may, through the use of a tube expander, be rolled and expanded tightly against the inside surface of the tube receiving holes for pressure tight engagement. With headers, such as the sinuous header, illustrated in FIG. 8, the bore 30 is so small as to be impassable to a man. Therefore, it is necessary to cut an elliptical hand hole 31 opposite the tube receiving hole to allow access for the tube expanding tool in order to roll the end of tube and expand it against the interior surface of the tube receiving hole in the header 17a. It is necessary to seal hand hole 31, through the use of a plate, a bolt 33 and nut 34 in engagement with a claim 32.

With time, welding techniques improved so that the hand hole could be eliminated by utilizing a strength weld. Therefore, by forming a cylindrical tube into a rectangular header, it was possible through socket welds 35, as illustrated in FIG. 9, to place the tubes either in in-line position or in staggered relation by forming a socket of uniform depth around each of the tube receiving holes in the fiat face of the rectangular header 17b.

This technique required considerable precision in cutting the tubes to length so that mill cut tubes could not be utilized.

A socket weld in a cylindrical header, as illustrated in FIG. 10, required a rather large diameter header 170 because of the curvature of the header. Thus, as is shown Patented June 2, 1970 in FIG. 11, the socket which under code requirements, was required to be of a particular depth 42, was much deeper at the vertical centerline 27 than at the lateral edge of the socket (as illustrated in FIG. 10) due to the headers curvature. Again, it was, of course, necessary to accurately cut the tubes so that each tube forming the bank would be of uniform length. Furthermore, a staggered tube connection with a cylindrical header, was diflicult to arrange. Another method of tube connection, illustrated in FIG. 12, was a double fillet weld connection in which the tube extended through the wall of the header and was welded into position with fillet welds 50 on the interior and exterior surface. However, this again required a hand hole 31 opposite the tube receiving hole which hand hole was subsequently closed by means of a plate and clamp.

SUMMARY OF THE INVENTION This invention relates to a new and novel Welded tube connection to upper and lower cylindrical headers forming a modular tube and header assembly. Basically, this invention involves the provision of one or more rows of tube receiving holes, bored through the header wall, parallel to the vertical centerline of the header in which each hole has a welding groove around its perimeter of essentially uniform depth. This invention contemplates the use of mill cut tube lengths in which the free ends of the tubes extend through said holes and project into the bore or internal cavity of the header. In a preferred embodiment, the header contains two rows of tube receiving holes, equally spaced from the vertical centerline of the header. Each hole has a welding groove on the exterior surface of said header wall, which is of substantially uniform depth and which surrounds the perimeter of said hole, the depth of said welding groove being equal to the wall thickness of the heat exchange tube and in any event, not less than one quarter of an inch. The tubes are welded into position so that their longitudinal axes are parallel to the vertical centerline of the upper and lower headers, respectively. Due to the staggered relationship of the holes and tubes relative to the holes and tubes of adjacent rows, it is possible to utilize finned tubes. The weld bonding the external wall of the header to the external wall of the tube is the only bonding means of the tube to the header and the tube is not bonded to the interior surface of the header but projects into the bore of the header.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a longitudinal sectional view, partially in elevation, illustrating an auxiliary fired, waste heat, water tube, natural circulation steam generator, the tubes being diagrammatically illustrated, without fins and in single rows for ease of illustration.

FIG. 2 is a diagrammatic perspective view illustrating a dual modular arrangement of tube banks, the tubes being diagrammatically illustrated without fins and in single rows for ease of illustration.

FIG. 3 is a fragmentary plan view of the header of this invention, illustrating the preferred staggered arrangement of the tubes.

FIG. 4 is an elevational view of the modular tube bank of this invention, so oriented that the upper header is on the left hand side of the page and the lower header is on the right hand side of the page.

FIG. 5 is a fragmentary, sectional view of the tubular header of this invention, illustrating the tube receiving holes surrounded by single bevel welding grooves.

FIG. 6 is a sectional view, taken along lines 6-6 of FIG. 5, illustrating the angle of the bevel of the welding groove, as well as the depth of the welding groove in the header wall.

FIG. 7 is a fragmentary sectional view, illustrating the 3 cylindrical tubular header of this invention and the welded tube connection wherein the free ends of the heat exchange tubes extend into the bore of the header.

FIG. 8 is a perspective view, illustrating a prior art sinuous rectangular header, used in marine type steam generators and containing hand holes and clamps.

FIG. 9 is a fragmentary sectional view of a prior art rectangular header and a socket welded tube connection.

FIG. 10 is a fragmentary sectional view of a prior art cylindrical header having a socket Welded tube connection along its vertical centerline.

FIG. 11 is a fragmentary side elevation, partially in section, of the header and tube connection of FIG. 10.

FIG. 12 is a fragmentary sectional view of a prior art cylindrical header, illustrating a fillet weld on the interior and exterior surfaces of the header around the perimeter of the tube.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now to the drawings, an auxiliary fired waste heat water tube natural circulation steam generator 1, in which the primary source of heat is the exhaust from a gas turbine (not shown) is illustrated in FIG. 1 in longitudinal section. An auxiliary burner raises the temperature of the gases leaving the gas turbine from about 900 F. to about 2000 F. in combustion zone 11.

A single row of vertically disposed high alloy tubes in communication with upper and lower headers 17 forms a bank 6 of screening tubes directly in front of two banks 7 of super heating tubes. The hot gases leaving the combustion zone 11 at about 2000 F. strike the banks 6 and 7 of heat exchange tubes and are cooled to a temperature of about 1000 F. as they enter the multiple banks 14 of vetrically upright heat exchange tubes forming the main evaporation section 23 of the steam generator 1.

Directly behind the multiple banks 14 of heat exchange tubes in the main evaporation section 23 is located a large water downcomer or feed pipe 44 which feeds water from steam and water drum 9 to feed header or lower water drum 12. It will be noted that the lower header 17, in communication with the bank of screening tubes 6, is in communication with the feed header 12 through feeder tubes 22. Additionally, each of the lower headers 17 forming the feed inlet for the banks 14 of heat exchange tubes in main evaporation section 23 are in communication via feeder tubes 22 with the feeder header 12.

Additionally, each of the upper headers 17, forming banks 14 of heat exchange tubes are in communication with the steam drum 9 by way of steam risers 20 so that the water and steam mixture entering the steam separation drum 9 is separated by means of steam separators into the gas and liquid phase.

Immediately behind the banks 14 of heat exchange tubes is a 3 to 4 bank multipass economizer 13 which absorbs the sensible heat from the gases leaving the main evaporation zone 23, so that the gases entering the main stack 45 are lowered to a temperature of about 350-400 F. By use of shop assembled banks of tube and header assemblies 6, 7, 13 and 14, respectively, utilizing headers 17 of identical diameter and the welded tube connection of this invention, the field erection time of a steam gen erator of the type illustrated can be markedly reduced.

Further, as is illustrated in FIG. 2, the modular tube banks of this invention lend exceptional flexibility in the fabrication and design of steam generators in that the capacity of the steam generator may be doubled by providing, as illustrated, dual evaporator sections 23 and dual economizer sections 13 arranged in parallel for large gas turbines. The evaporating and economizing sections 23 and 13, respectively, are shop assembled and shipped to the erection site in sections. At the erection site, the steam risers are field connected to the steam drum 9 from each of the headers 17. The economizer connection 46 from the header 17 is made to the steam drum 9 in the field so that the field erection time is markedly reduced from conventional steam generator fabrication practice. Further, it will be apparent that the evaporating sections 23 can be increased or decreased in increments of the capactiy of one bank 14 of heat exchange tubes without a substantial redesign of the steam generator. Shop assem bled feeder tubes 22, connected in the shop to the feed header 12 are schematically illustrated.

As is indicated in FIG. 3, the row of tube receiving holes 25 and row 26 f tube receiving holes are equidistantly spaced from the vertical centerline 27 of the header 17 so that there is a ligament 28 between adjacent holes in the same row and a ligament 29 between adjacent holes in adjacent rows.

FIG. 4 illustrates a bank of tubes 14 in which the individual finned tubes 15 communicate with upper and lower headers 17. The upper and lower headers 17 are closed at each end by end plates, not shown, and spacers 18 are used to mount the tube bank 14 into proper position. The upper header 17 contains a steam drum support 21 and steam risers 20 which communicate with the steam and water drum 9. The lower header 17 contains two feeder tubes 22 communicating with the lower feed header or water drum 12.

Referring now to FIGS. 5, 6 and 7, the preferred header 17 is shown in fragmentary section, which consists of tube receiving holes 25 and 26 surrounded by a welding groove 38. Each of the holes 25 and 26 are bored through the header wall parallel to the vertical centerline 27 of the header 17 and are laterally spaced from the vertical centerline to allow for a staggered placement of finned tubes. The lateral placement of the holes, however, complicates provision of the groove 38, since the depth 42 and angle 41 of the groove 38 should be uniform around the perimeter of each hole. As contrasted with the placement of the socket on the vertical centerline as illustrated in FIG. 10, the full curvature 40 is involved in the depth of the groove because of its lateral placement. Welding groove 38 provides the basis of a good bond in the form of a combination groove and fillet weld 43 which bonds the exterior wall of the tubes 15 to the exterior wall of the header 17 and allows the free ends of the tubes 15 to project into the bore 30 of the header 17. For this reason, mill cut tubes may be utilized since an exacting tolerance is not required. The staggered arrangement of holes 25 and 26 allows for good ligament strength 29 between the holes in adjacent rows and allows for the provision of fins 16 on the heat exchange tubes 15 for maximum heat transfer surface.

Uniformity in depth of the beveled welding groove 38 can be obtained by the use of a carbon arc torch or by use of a specially designed cutting tool, designed to cut into the exterior wall of the header 17 around holes 25 and 26 despite the curvature 40 of the tubular cylindrical header 17.

This preferred method of tube connection may be compared with the socket weld 35 illustrated in FIGS. 9 and 10 or with the external and internal fillet weld illustrated in FIG. 12. The external and internal fillet weld 50 is acceptable in providing sufficient strength. However, it again requires the provision of a hand hole 31.

By use of the preferred method of tube connection, described herein, substantial economies in time and labor may be eifected since excessively fine tolerances are not required, thus, allowing the use of mill cut tubes. There is no necessity for bending the tubes to approach the header radially and the provision of a hand hole is not required. Thus, by selection of a suitable diameter header and suitable diameter heat exchange tubes, banks of either finned or bare tubes may be shop assembled and placed in inventory so as to be available for the fabrication of a steam generator of a given capacity. The capacity of the steam generator is exceedingly flexible and it may be doubled by provision of dual evaporating and economizing sections or may be increased or decreased incrementally according to the output of one bank of heat exchange tubes.

What is claimed is:

1. For use in a steam generator, including a series of banks of shop assembled heat exchange tubes,

(A) a welded header and tube assembly comprising:

(1) a cylindrical tubular header having a row of tube receiving holes, each hole extending through the wall of said header parallel to the vertical centerline of said header, and,

(a) a welding groove on the exterior surface of the wall of said header, around the perimeter of each of said holes;

(2) a row of heat exchange tubes, equal in number to the number of tube receiving holes, in which the free ends of said tubes project through the holes in the wall of said header parallel to the vertical centerline of said header to communicate with the bore of said header; and

(3) a weld in each of said grooves bonding the wall of said header to the wall of each of said tubes.

2. A welded header and tube assembly, as defined in claim 1, in which:

(A) said welding groove is of uniform depth around the perimeter of said hole.

3. A welded header and tube assembly, as defined in claim 1, in which:

(A) said welding groove has a minimum depth at any point around the perimeter of said hole, equal to the wall thickness of said heat exchange tube and not less than one quarter of an inch.

4. A welded header and tube assembly, as defined in claim 1, in which:

(A) said weld is a combination groove and fillet weld.

5. A welded header and tube assembly, as defined in claim 1, in which:

(A) the longitudinal axes of said heat exchange tubes are parallel to the vertical centerline of said header.

6. A welded header and tube assembly, as defined in claim 1, in which:

(A) said row of tube receiving holes is laterally spaced from the vertical centerline of said header.

7. A welded header and tube assembly, as defined in claim 6, the further combination therewith of:

(A) a second row of tube receiving holes in said header, said second row being laterally spaced from said vertical centerline so as to be equidistantly placed from said vertical centerline relative to the other row of tube receiving holes,

(1) each of said holes extending through the wall of said header parallel to the vertical centerline of said header, and

(2) a welding groove on the exterior surface of the wall of said header around the perimeter of each of said holes;

(B) a second row of heat exchange tubes, equal in number to the number of said tube receiving holes in said second row, in which the free ends of said tubes project through the holes in the wall of said header parallel to the vertical centerline of said header to communicate with the bore of said header, and

(C) a weld in each of said grooves bOnding'the wall of said header to the wall of each of said tubes.

8. A welded header and tube assembly, as defined in claim 7, in which the location of holes in one row is staggered in relation to the location of holes in the second row.

9. A welded header and tube assembly, as defined in claim 8, in which the ligament between adjacent holes in one row is equal to the ligament between adjacent holes in the second row.

10. A welded header and tube assembly, as defined in claim 8, in which the ligament between adjacent holes in the same row is at least equal to the ligament between adjacent holes in adjacent rows.

References Cited UNITED STATES PATENTS 1,350,200 8/1920 Yarrow 122-365 2,555,043 5/1951 Lewis 122-7 2,754,807 7/1956 Smith 1227 3,003,482 10/ 1961 Hamilton et al 122-478 3,291,962 12/1966 Walker 122511 XR FOREIGN PATENTS 612,442 7/1926 France.

KENNETH W. SPRAGUE, Primary Exmainer UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Pat nt 3.515.101 Dated June 2. 1970 Inventor(s) Warner V. Hambleton and Dean P. LJnthank It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

ln the address of Warner V. l-lambleton for "Dallas" read Spring Col. 4, line 10, after "26" for "i" read of Col. 5, line 7, after "having" insert an internal bore with an internal diameter sufficiently small to be impassable to a man and having Col. 5, line 9, after "header" insert with the vertical walls of said hole being Col. 5, line 18, insert after "header" and extend into the bore of said header Col. 5, line 20-, for "a weld in each of said grooves" read means Col. 5, line 22, strike the period and add consisting of only a weld in said welding groove.

Col. 6, line 7, insert after "header" with the vertical walls of said holes being Col. 6, line 16, after "header"(first occurrence) insert and extend into the bore of said header Col. 6, line 19, for "a weld in each of said grooves" read means Col. 6, line 20, strike the period and add consisting of only a weld in said welding groove was Afloat:

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